meanwhile, investigators are trying to determine if there s a link between the other suspected bomber, tamerlan tsarnaev, and this man, william plotnikov, a canadian boxer turned jihadist. he was killed last year in a shootout with russian troops. that happened in dagestan while tamerlan tsarnaev was in the region. the investigation of the tsarnaev brothers has put southern russia on the map for a lot of people. investigators right now taking a hard look at dagestan and chechnya. a disturbing trend in that part of the world. the rise of women suicide bombers. known as black wid dowidows. nic robertson reports from dagestan. reporter: in dagestan s capital last may, an inferno, moments earlier, a female suicide bomber known here as a black widow, detonated a bomb at a police checkpoint.